Silk use during proecdysis in the spider Araneus cavaticus (Araneae: Araneidae)

Major ampullate (MaA) and minor ampullate (MiA) silk glands of juvenile Araneus cavaticus were examined by dissection at various times relative to ecdysis. Several days before ecdysis the single, larger pairs of MaA and MiA glands (termed \u27primary\u27 MaA and MiA glands) become non-functional and remain so until ecdysis. Nevertheless, proecdysial spiders are able to draw ampullate fibers due to the presence of smaller pairs of MaA and MiA glands (termed \u27open secondary\u27 MaA and MiA glands) which are functional at this time. It appears that these open secondary MaA and MiA glands are intended for use only during proecdysis. Thus, primary MaA and MiA glands and open secondary MaA and MiA glands are typically not used concurrently (a brief transitional period is an exception). The open secondary MaA and MiA glands functioning in one juvenile stadium become \u27blocked secondary\u27 MaA and MiA glands in the following stadium, during which they regress and are non-functional. (Glands referred to in the past as \u27accessory\u27 MaA and MiA glands are secondary MaA and MiA glands while in their more regressed form.) These blocked secondary MaA and MiA glands do not re-develop into functional open secondary MaA and MiA glands until the following stadium. Thus, a given pair of secondary MaA or MiA glands is only functional in every other juvenile stadium. However, because there are two sets of secondary MaA and MiA glands (each set consisting of one pair of secondary MaA glands and one pair of secondary MiA glands) which function alternately, the spider is able to produce ampullate fibers during the proecdysial portion of each stadium. Cuticular protuberances known as nubbins and tartipores exist in proximity to spigots in many spiders, including A. cavaticus. As defined herein, the former appear to be vestigial spigots. Tartipores, on the other hand, are formed because the new cuticle which develops beneath the old cuticle during proecdysis has to leave openings for the ducts of those silk glands that will function during proecdysis. After ecdysis, the \u27collars\u27 that had formed around these ducts remain in the new cuticle, in collapsed form, as tartipores